Available for projects · Remote

Most Shopify stores are built to launch.
I build them to last.

9+ years working exclusively on Shopify: architecture decisions that hold under scale, migrations that don't break what's already working, and performance engineering tied to real metrics.

Let's talk → See my work ↓

9+ years exclusively on Shopify

3+ years with twothirds.com

5+ years with ff.md

15+ international markets configured

Selected work

Real stores. Real scale.

Not demos. Not generic implementations. Projects where architecture decisions had actual consequences for revenue, performance, and longevity.

3-year technical partnership · Sustainable Fashion · B Corp

twothirds.com

3+ years as technical partner for a B Corp-certified sustainable fashion brand (325k+ subscribers, 14k+ Trustpilot reviews). Full manual migration from OS 1.0 to 2.0: section-by-section rebuild, not a template swap. International expansion across 15+ markets, B2B wholesale, Klaviyo integration, Core Web Vitals. The kind of relationship where architecture decisions actually have consequences.

325k+ subscribers

14k+ Trustpilot reviews

15+ markets configured

3+ years ongoing

OS 1.0 → 2.0 Migration Shopify Markets B2B Wholesale Core Web Vitals Klaviyo Liquid

eCommerce platform · Pharmacy · Moldova · Since 2020

ff.md

Built the online store for Moldova's largest pharmacy chain from scratch, and have been their technical partner since 2020. 30,000+ products, custom one-page checkout, fully automated backend connected via APIs. Custom theme architected and implemented for pharmaceutical-grade catalog management at scale.

Custom Theme 30k+ Products Custom Checkout API Automation Liquid

Full Replatform · WooCommerce → Shopify · Launched 2026

smilemobile.ro

New and refurbished phones out of Cluj-Napoca. Replatformed the whole business solo: custom OS 2.0 theme, custom migration toolkit, AI-assisted content pipeline, SEO carried over URL by URL. Launched June 2026.

WooCommerce → Shopify Custom Theme Migration Toolkit SEO

Performance Rebuild · Premium Brand

Performance rebuild

Premium brand whose store had slowed to a crawl. Theme rebuilt from scratch, LCP cut in half. Now self-managed on a foundation that holds.

Performance Theme Architecture Core Web Vitals

Shopify Plus · Haute Parfumerie · Luxury

edel.co

Shopify Plus redesign for an haute parfumerie brand (Eulalia de Lucia). Full theme build covering homepage, product pages, collection views, mobile experience and cart, all designed to match a complete brand relaunch.

Shopify Plus Custom Theme Luxury Brand Design-Led

Shopify App Store

Apps I've built and published.

Building apps means understanding both sides: what the merchant actually needs, and what makes an app good enough to survive Shopify's review process.

Live on App Store

COS ‑ Social Share Images

Generates and customizes Open Graph images for all Shopify resource types via a template-based UI. No coding required. Built to Shopify's highest standards for performance, design, and OS 2.0 integration.

React / Polaris Node.js OS 2.0 Extensions Open Graph

View on Shopify App Store →

UI Contribution

Schema Breadcrumbs

Built the full admin interface for this published Shopify app: structured data and breadcrumb schema injection for SEO. Delivered using Shopify Polaris and React, following Shopify's embedded app standards.

React / Polaris Shopify Embedded App Structured Data SEO

View on Shopify App Store →

In development

Bundles & Discounts

Bundles, cart offers and discounts for Shopify, built on native discount stacking with Rust Shopify Functions compiled to WASM. Storefront widgets ship through a theme extension. Co-developed with a partner, heading for the App Store.

React Router Shopify Functions Rust / WASM Prisma Theme Extension

Not published yet

In development

COS SEO

Rewrites product SEO from a Context Pack distilled out of the merchant's own documents. Deterministic guards catch fabricated output before it ships, every write needs human approval, and updates are field-surgical: they never touch what the team edits by hand.

Remix / Polaris Anthropic API Context Distillation Prisma

Not published yet

What I do

Senior-level work for serious Shopify stores.

I don't take isolated tasks. I take on problems that require architectural thinking, and I stay until they're solved properly.

🏗

Theme Architecture

OS 2.0 section/block systems, metafields, metaobjects. Built to last, not to demo.

⚡

Performance Engineering

Core Web Vitals tied to real metrics. Custom build tooling, lazy loading, bfcache.

🔄

Platform Migrations

Manual OS 1.0 → 2.0 migrations that preserve what's working. No shortcuts.

🌍

Shopify Markets

Multi-region setup, localized content, payment methods, tax and shipping rules.

🧩

App Development

Custom apps with React/Polaris, Node.js, built to pass Shopify's review process.

🔗

API & Integrations

Storefront API, GraphQL, Checkout Extensions, Shopify Flow, Webhooks.

Catalin Costinas
Senior Shopify Architect
Cluj-Napoca, Romania · Remote

About

9+ years.
One platform. Depth by design.

I've been working exclusively on Shopify since 2016. Not across five platforms. Not as a side skill. This is the only thing I do, and that depth is what separates the work.

I specialize in the layer most developers skip: architecture decisions that hold under scale, migrations that don't break what's already working, and performance engineering tied to real metrics, not just Lighthouse scores.

In practice, that means a 3-year technical partnership with twothirds.com, a B Corp-certified sustainable fashion brand with 325k+ subscribers and 14k+ Trustpilot reviews. Full manual OS 1.0 → 2.0 migration, international expansion across 15+ markets, B2B wholesale, Klaviyo integration, ongoing performance engineering.

It means building ff.md from scratch in 2020, the online platform for Moldova's largest pharmacy chain, and staying as their technical partner ever since. 30,000+ products, custom one-page checkout, fully automated backend via APIs.

And it means building and publishing my own apps on the Shopify App Store: understanding both what merchants actually need from an app, and what it takes to pass Shopify's review process.

The clients I work with don't need someone to install a theme. They need someone who knows when the easy option will cost them six months later.

Liquid OS 2.0 Metafields / Metaobjects React / Polaris Node.js Shopify Remix Storefront API GraphQL Shopify Markets Core Web Vitals Klaviyo PostgreSQL / Prisma OpenAI API esbuild / Vite

If you're building something serious
on Shopify, let's talk.

Not looking for task-based freelancing. Looking for the kind of problem where architecture actually matters.

hello@costinas.com →

LinkedIn Shopify Partner

Most Shopify stores are built to launch. I build them to last.